"I want a trial for moral, legal and security reasons," said Nicolas Henin, who was reporting for French magazine Le Point in Syria when he was captured and held by ISIS for 10 months.

Henin told NBC News on Friday that he wouldn't "be at ease as long as European jihadists are detained in prisons" in the Middle East, where legal standards "are not those of the Western world" and where there are opportunities to escape "by force or through corruption."

The journalist said it is crucial that the two men are given a fair trial as doing otherwise would "offer them the chance to present themselves as victims."

American officials on Thursday identified the two "Beatles" captured on the battlefield last month by U.S.-backed Syrian Democratic Forces as Alexandar Amon Kotey and El Shafee Elsheikh. The best-known member of the group was Mohammed Emwazi, who was nicknamed "Jihadi John" and seen in propaganda videos beheading hostages. He was killed in an airstrike in Raqqa, Syria, in November 2015. The fourth member, Aine Davis, is in Turkish custody. All four men originally hailed from West London.

Henin was released by ISIS in April 2014 alongside fellow French journalists Didier Francois, Edouard Elias and Pierre Torres.

Speaking to French radio station Europe 1 on Friday, Francois described Kotey as "the preacher of the group" and Elsheikh as "an absolute psychopath."

He said "The Beatles" tended to be "our most violent guards, keen on systematic torture and partial to techniques such as drowning and suffocation but not only. They also loved mock executions and crucifixions."

Francois added: "As soon as they entered our cell, blows would rain down on us. They hit hard and as they loved doing that, it could go for a long time."